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Here’s Lee Billings at New Scientist coming to the point with admirable swiftness:

Two decades of searching have failed to turn up another planetary system like ours. Should we be worried?- “No place like home: Our lonesome solar system” (11 May 2011)

He answers his own question, in part:

It was clear we had ignored a fundamental rule of science. “We had been judging the cosmic diversity of planetary systems based on a sample size of one,” says Marcy.
If these were the first hints that our solar system was not normal, they were not the last. Other planets were soon caught breaking all sorts of rules: orbiting in the opposite direction to their star’s spin, coming packed in close orbits like sardines in a can, or revolving on wildly tilted orbits far away from their star’s equator.

Soon “theorists began to supply the necessary creation stories.”
Billings brings us up to date on how planets are detected, then comes the punch line:

All this makes the status of our solar system increasingly clear. “Our system is a rarity, there’s no longer a question about that,” says Marcy. “The only question that remains is, just how rare is it?”

When all of these factors occur together, they create a region of space that Gonzalez calls a “Galactic Habitable Zone.” Gonzalez believes every form of life on our planet – from the simplest bacteria to the most complex animal – owes its existence to the balance of these unique conditions.Because of this, states Gonzalez, “I believe both simple life and complex life are very rare, but complex life, like us, is probably unique in the observable Universe.”
- Leslie Mullen, “Galactic Habitable Zones,” Astrobiology Magazine, 05/18/01

Gonzalez was then Assistant Professor of Astronomy at the University of Washington (1999-2001). Mullen’s decade-old article is free of the hostility that later dogged Gonzalez when, at Iowa State University,

After the release of Privileged Planet, ISU religious studies professor Hector Avalos–faculty advisor to the campus Atheist and Agnostic Society–began publicly campaigning against Dr. Gonzalez and his work. Although Dr. Gonzalez had never introduced intelligent design into his classes, Avalos helped spearhead a faculty petition urging “all faculty” at ISU to “uphold the integrity of our university” by “reject[ing] efforts to portray Intelligent Design as science.” Avalos later conceded to a local newspaper that Gonzalez was the key motive for the petition. The logical conclusion of this campaign against Dr. Gonzalez came in the spring of 2007, when ISU President Gregory Geoffroy denied Dr. Gonzalez’s application for tenure.

Avalos’ success has been widely considered a great victory for “science.”

What about within this solar system (and not necessarily a planet but also a moon)?

Find life and then we will no longer be unique and at the same time we would have to reconsider the possibility that we are rare if scientists could prove that the DNA in both places had separate origins.

“Be polite, be professional, but have a plan to kill everybody you meet.”
James "Mad Dog" Mattis

I think its still only anybody's best guess as to whether earth-like planets are rare or not. We can pretend like we've made some significant progress by making all these lists of criteria, like galactic inhabitable zones, for planets habitable for life, etc... but we simply have no idea if any of it holds, since our sample size of known planets is so small.

Its unclear which philosophical camp gains an advantage if Earth is rare or not. Atheist/theists can use either position to sort of support their views. eg, If Earth is rare, obviously the universe is not fine tuned for life.. or if Earth is rare, obviously it is fine tuned for human existence, etc.

Its unclear which philosophical camp gains an advantage if Earth is rare or not. Atheist/theists can use either position to sort of support their views. eg, If Earth is rare, obviously the universe is not fine tuned for life.. or if Earth is rare, obviously it is fine tuned for human existence, etc.

yes, but they can not explain how the Earth is in the PERFECT place in the galaxy and solar system for life to be supported, until life is found that lives outside these areas at proves it otherwise,